When i execute the following Script. I get error 'Cannot roll back InnerTran. No transaction or savepoint of that name was found.' i.e I couldn't able to rollback inner transaction.Can any one know the reason for this?

So we cannot have nested Transactions (it does not make any sense to have nested transaction when we are not allowed to rollback the inner transaction) in SQL Server? And if we want nested transaction we should use Save Point instead?

In other words in SQL Server nested transactions can be implemented by using Save Points? Kindly explain this.